Long Term Evolution (LTE) wireless communication technology uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)-spread OFDM in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. In the time domain, LTE downlink transmissions are organized into radio frames of ten milliseconds (ms), each radio frame consisting of ten equally-sized subframes of length TSUBFRAME=1 ms, as illustrated in FIG. 2.
Furthermore, resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. A pair of two adjacent resource blocks in time direction (1.0 ms) is known as a resource block pair. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
The notion of Virtual Resource Blocks (VRBs) and Physical Resource Blocks (PRBs) has been introduced in LTE. The actual resource allocation to a User Equipment (UE) is made in terms of VRB pairs. There are two types of resource allocations, localized and distributed. In the localized resource allocation, a VRB pair is directly mapped to a PRB pair, hence two consecutive and localized VRBs are also placed as consecutive PRBs in the frequency domain. On the other hand, the distributed VRBs are not mapped to consecutive PRBs in the frequency domain, thereby providing frequency diversity for a data channel transmitted using these distributed VRBs.
Downlink transmissions are dynamically scheduled. Specifically, in each downlink subframe, the base station transmits Downlink Control Information (DCI) that indicates the UEs to which data is transmitted in the current subframe and upon which resource blocks the data is transmitted to those UEs in the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3, or 4 OFDM symbols in each subframe, and the number n=1, 2, 3, or 4 is known as the Control Format Indicator (CFI). The downlink subframe also contains common reference symbols, which are known to the receiver and used for coherent demodulation of, e.g., the control information. A downlink subframe with CFI=3 OFDM symbols as control is illustrated in FIG. 3. From LTE Release 11 onwards, the above described resource assignments can also be scheduled on the Enhanced Physical Downlink Control Channel (EPDCCH). For Release 8 to Release 10, only the Physical Downlink Control Channel (PDCCH) is available.
Current LTE networks (i.e., LTE Releases up to Release 11) support three modulation schemes: Quadrature Phase-Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (QAM), and 64QAM. However, next generation and future generation LTE networks desire to support higher order modulation schemes (e.g., 256QAM). Supporting these higher order modulation schemes can significantly increase the implementation complexity and cost both of the LTE network as well as the UEs. Thus, there is a need for systems and methods for supporting, e.g., 256QAM in an LTE network in a manner that is efficient in terms of complexity and cost of implementation.